Inverter circuits are increasingly being used to control a wide variety of electrical equipment to conserve energy and achieve high efficiency from the viewpoint of environmental protection. In particular, in the car industry, the development of technologies for conserving energy and improving efficiency to reduce impact on global environment continues to gather momentum. This includes commercialization of hybrid electric vehicles (hereinafter referred to as HEVs) powered by an electric motor plus a gasoline engine.
The service voltage range of the electric motor for these HEVs is as high as several hundred volts, and thus metallization film capacitors are of increasing interest for use in these electric motors due to their high withstand voltage and low loss. In addition, metallization film capacitors have an extremely long service life, so they also tend to be adopted on the market for reasons of low maintenance.
For use in vehicles, high heat resistance and high withstand voltage are needed in metallization film capacitors, and thus a range of developments and proposals have been made with this goal in mind.
FIG. 4 is a perspective view of a structure of a conventional metallization film capacitor. As shown in FIG. 4, first metalized film 21 is configured by metalizing the surface of first dielectric film 22, typically a polypropylene film, with electrode film 23. Electrode film 23 is not formed on margin 22a. Electrode film 23 is not also formed on cross-shaped first slit 22b. Segments 23a, which are unit capacitors whose functional area is segmented, are each connected to first fuse 23b. Second fuse 23c couples the deposited electrodes on functional areas separated by second slit 22c to deposited electrodes on electrode lead-out areas. Second slit 22c, on which no electrode film is formed, extends lengthwise along the film.
Second metalized film 24 includes second dielectric film 25, margin 25a, cross-shaped first slit 25b, second slit 25c, electrode film 26, segment 26a, first fuse 26b, and second fuse 26c, the same as the first metalized film. In addition, this metallization film capacitor has metal-sprayed portions 27 and 28 for lead-outs.
In a conventional metallization film capacitor as configured above, multiple single-element capacitors form numerous unit capacitors, and a fuse is provided between unit capacitors and between the functional area of capacitor and the electrode lead-out area. If any abnormality arises, the function of the capacitor is secured by the fuse blowing to minimize capacity reduction without causing insulation breakdown. Even in an abnormality in which short-circuit current caused by insulation breakdown cannot be shut off by the first fuse, the functional area of the capacitor and the electrode lead-out area can be cut off by the second fuse so as to reliably avoid a short-circuit failure. This significantly improves reliability against insulation breakdown. Accordingly, a small and light capacitor with significantly improved reliability with respect to insulation performance can be provided, compared to the conventional capacitor.
Prior art related to the present invention is typically disclosed in Patent Document 1.
An electrode pattern formed by metal deposition in the above conventional metallization film capacitor significantly improves reliability against insulation breakdown by the fuse blowing if an abnormality occurs so that insulation breakdown can be prevented, minimizing capacity reduction. However, the heat resistance of a conventional metallization film capacitor is low (about 110° C.) because it generally uses a polypropylene film (hereafter referred to as a “PP film”) for its dielectric film. This does not achieve resistance to the high temperature (150° C.) needed for vehicles.
To improve heat resistance, one method is to use a dielectric film containing an inorganic filler, such as polyethylene naphthalate (hereafter referred to as “PEN”), polyphenylene sulfate (hereafter referred to as “PPS”), and polyethylene terephthalate (hereafter referred to as “PET”). However, if a PEN film is used, sufficient heat resistance is achieved, but the withstand voltage is low. Performance of withstand voltage is not sufficient even if electrode patterns are formed by metal deposition, a technology built on the use of conventional PP film.    Patent Document 1: Japanese Patent Unexamined Publication No. H8-250367.